]> Arm Limited

Brendan.Moran.ietf@gmail.com

Security SUIT Internet-Draft This specification describes extensions to the SUIT manifest format defined in . These extensions allow an update author, update distributor or device operator to more precisely control the distribution and installation of updates to IoT devices. These extensions also provide a mechanism to inform a management system of Software Identifier and Software Bill Of Materials information about an updated device.

Introduction Full management of software updates for unattended, connected devices, such as Internet of Things devices requires a cooperation between the update author(s) and management, distribution, policy enforcement, and auditing systems. This specification provides the extensions to the SUIT manifest () that enable an author to coordinate with these other systems. These extensions enable authors to instruct devices to examine update priority, local update authorisation, update lifetime, and system properties. They also enable devices to report and distributors to collect Software Bill of Materials information. Extensions in this specification are OPTIONAL to implment and OPTIONAL to include in manifests unless otherwise designated.

Conventions and Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. Additionally, the following terminology is used throughout this document: SUIT: Software Update for the Internet of Things, also the IETF working group for this standard.

Extension Metadata Some additional metadata makes management of SUIT updates easier: CoSWID, CoMID, CoRIM Text descriptions of requirements

suit-coswid a CoSWID can enable Software Bill-of-Materials use-cases. A CoMID can enable monitoring of expected hardware. A CoRIM (which may contain both CoSWID and CoMID) can enable both of these use-cases, but can also act as the transport for expected values to an attestation Verifier. Tightly coupling update and attestation ensures that verification infrastructure always knows what software to expect on each device. suit-coswid is a member of the suit-manifest. It contains a Concise Software Identifier (CoSWID) as defined in . This element SHOULD be made severable so that it can be discarded by the Recipient or an intermediary if it is not required by the Recipient. suit-coswid typically requires no processing by the Recipient. However all Recipients MUST NOT fail if a suit-coswid is present. suit-coswid is RECOMMENDED to implement and RECOMMENDED to include in manifests. NOTE: CoRIM comprises a list of CoSWID and a list of CoMID, so it may be preferable to a CoSWID. NOTE: CoMID may be a preferable alternative to Vendor ID/Class ID, however it consumes more bandwidth, so a UUID based on CoMID may be appropriate.

text-version-required suit-text-version-required is used to represent a version-based dependency on suit-parameter-version as described in and . To describe a version dependency, a Manifest Author SHOULD populate the suit-text map with a SUIT_Component_Identifier key for the dependency component, and place in the corresponding map a suit-text-version-required key with a free text expression that is representative of the version constraints placed on the dependency. This text SHOULD be expressive enough that a device operator can be expected to understand the dependency. This is a free text field and there are no specific formatting rules. By way of example only, to express a dependency on a component "['x', 'y']", where the version should be any v1.x later than v1.2.5, but not v2.0 or above, the author would add the following structure to the suit-text element. Note that this text is in cbor-diag notation.

=1.2.5,<2" } ]]>

Extension Parameters Several parameters are needed to define the behaviour of the commands specified in . These parameters follow the same considerations as defined in Section 8.4.8 of . Name CDDL Structure Reference Use Before suit-parameter-use-before Minimum Battery suit-parameter-minimum-battery Update Priority suit-parameter-update-priority Version suit-parameter-version Wait Info suit-parameter-wait-info Component Metadata suit-parameter-component-metadata

suit-parameter-use-before An expiry date for the use of the manifest encoded as the positive integer number of seconds since 1970-01-01. Implementations that use this parameter MUST use a 64-bit internal representation of the integer. Used with

suit-parameter-minimum-battery This parameter sets the minimum battery level in mWh. This parameter is encoded as a positive integer. Used with suit-condition-minimum-battery ().

suit-parameter-update-priority This parameter sets the priority of the update. This parameter is encoded as an integer. It is used along with suit-condition-update-authorized () to ask an application for permission to initiate an update. This does not constitute a privilege inversion because an explicit request for authorization has been provided by the Update Authority in the form of the suit-condition-update-authorized command. Applications MAY define their own meanings for the update priority. For example, critical reliability & vulnerability fixes MAY be given negative numbers, while bug fixes MAY be given small positive numbers, and feature additions MAY be given larger positive numbers, which allows an application to make an informed decision about whether and when to allow an update to proceed.

suit-parameter-version Indicates allowable versions for the specified component. Allowable versions can be specified, either with a list or with range matching. This parameter is compared with version asserted by the current component when suit-condition-version () is invoked. The current component may assert the current version in many ways, including storage in a parameter storage database, in a metadata object, or in a known location within the component itself. The component version can be compared as: Greater. Greater or Equal. Equal. Lesser or Equal. Lesser. Versions are encoded as a CBOR list of integers. Comparisons are done on each integer in sequence. Comparison stops after all integers in the list defined by the manifest have been consumed OR after a non-equal match has occurred. For example, if the manifest defines a comparison, "Equal [1]", then this will match all version sequences starting with 1. If a manifest defines both "Greater or Equal [1,0]" and "Lesser [1,10]", then it will match versions 1.0.x up to, but not including 1.10. While the exact encoding of versions is application-defined, semantic versions map conveniently. For example, 1.2.3 = [1,2,3]. 1.2-rc3 = [1,2,-1,3]. 1.2-beta = [1,2,-2]. 1.2-alpha = [1,2,-3]. 1.2-alpha4 = [1,2,-3,4]. suit-condition-version is OPTIONAL to implement. Versions SHOULD be provided as follows: The first integer represents the major number. This indicates breaking changes to the component. The second integer represents the minor number. This is typically reserved for new features or large, non-breaking changes. The third integer is the patch version. This is typically reserved for bug fixes. The fourth integer is the build number. Where Alpha (-3), Beta (-2), and Release Candidate (-1) are used, they are inserted as a negative number between Minor and Patch numbers. This allows these releases to compare correctly with final releases. For example, Version 2.0, RC1 should be lower than Version 2.0.0 and higher than any Version 1.x. By encoding RC as -1, this works correctly: [2,0,-1,1] compares as lower than [2,0,0]. Similarly, beta (-2) is lower than RC and alpha (-3) is lower than RC.

suit-parameter-wait-info suit-directive-wait () directs the manifest processor to pause until a specified event occurs. The suit-parameter-wait-info encodes the parameters needed for the directive. The exact implementation of the pause is implementation-defined. For example, this could be done by blocking on a semaphore, registering an event handler and suspending the manifest processor, polling for a notification, or aborting the update entirely, then restarting when a notification is received. suit-parameter-wait-info is encoded as a map of wait events. When ALL wait events are satisfied, the Manifest Processor continues. The wait events currently defined are described in the following table. Name Encoding Description suit-wait-event-authorization int Same as suit-parameter-update-priority suit-wait-event-power int Wait until power state suit-wait-event-network int Wait until network state suit-wait-event-other-device-version See below Wait for other device to match version suit-wait-event-time uint Wait until time (seconds since 1970-01-01) suit-wait-event-time-of-day uint Wait until seconds since 00:00:00 suit-wait-event-time-of-day-utc uint Wait until seconds since 00:00:00 UTC suit-wait-event-day-of-week uint Wait until days since Sunday suit-wait-event-day-of-week-utc uint Wait until days since Sunday UTC suit-wait-event-other-device-version reuses the encoding of suit-parameter-version-match. It is encoded as a sequence that contains an implementation-defined bstr identifier for the other device, and a list of one or more SUIT_Parameter_Version_Match.

suit-parameter-component-metadata In some instances, a system may need to know the file metadata for a component. This metadata can include: creator creation time modification time default permissions (rwx) a map of user/permission pairs a map of role/permission pairs a map of group/permission pairs file type Component metadata is applied at time of fetch, copy, or write; see , sections 8.4.10.4, 8.4.10.5, 8.4.10.6. Therefore, the component metadata parameter must be set in advance of the component being fetched, copied into, or written.

Creator Sometimes, management of file systems requires that the creator of each file is correctly recorded. Because the default creator of files will be the update agent, this can obscure the actual creator of each file. The Creator metadata element allows overriding the default behaviour and setting the correct creator. The creator is defined as follows:

The actor ID can be whatever is most appropriate for any given system. For example, the actor ID might be a string (e.g., username), integer (e.g., POSIX userid), or UUID (e.g., TEEP TA UUID).

Creation & Modification Time The creation and modification times are defined by CBOR time types. These are defined in , Section 3.4.2. The CBOR tag is REQUIRED when either creation or modification time are provided.

#6.1(uint) suit-meta-creation-time => #6.1(uint) ]]>

Component Default Permissions Typical permissions management systems require read, write, and execute permissions that are applied to all users who do not have their own explicit permissions. These are the default permissions for the current component. Default permissions are described by the following CDDL:

User, Role, Group permissions Many filesystems have users and groups. Additionally some have roles. Actors that have these associations can have specific permissions associated with them for each component. Each of these sets of permissions is defined the same way: with a map of actor identifiers to permissions.

SUIT_meta_permissions } ]]>

The SUIT_meta_actor_id is the same as defined for Creator, .

File Type File Type typically identifies whether a file is a directory, regular file, or symbolic link. If not specified, File Type defaults to regular file. This enables specific management operations for SUIT command sequences: To create a directory Set the Component Index to the Component Identifier of the directory to be created Set the Component metadata, including the file type for directory Set suit-parameter-content to an empty bstr Invoke suit-directive-write To create a symbolic link Set the Component Index to the Component Identifier of the link to be created Set the Component metadata, including the file type for symbolic link Set suit-parameter-content to the link target Invoke suit-directive-write For example, the following Payload Fetch & Install sequences will create a new /usr/local/bin directory, download https://cdn.example/example3.bin into a new file: /usr/local/bin/example3, then create a symlink at /usr/bin/example that points to /usr/local/bin/example3. Common has components for: /usr/bin/example /usr/local/bin /usr/local/bin/example3 Payload fetch: set component index = 1 set parameters: content = h'' metadata = {file-type: directory} write set component index = 2 set URI = "https://cdn.example/example3.bin" fetch condition image digest Install: set component index = 0 set parameters: content = "/usr/local/bin/example3" metadata = {file-type: symlink} write

Extension Commands The following table defines the semantics of the commands defined in this specification in the same way as in the Abstract Machine Description, Section 6.4, of . Command Name CDDL Identifier Semantic of the Operation Use Before suit-condition-use-before assert(now() < current.params[use-before]) Check Image Not Match suit-condition-image-not-match assert(not binary-match(digest(current), current.params[digest])) Check Minimum Battery suit-condition-minimum-battery assert(battery >= current.params[minimum-battery]) Check Update Authorized suit-condition-update-authorized assert( isAuthorized( current.params[priority])) Check Version suit-condition-version assert(version_check(current, current.params[version])) Wait For Event suit-directive-wait until event(arg), wait Override Multiple suit-directive-override-multiple components[i].params[k] := v for-each k,v in d for-each i,d in arg Copy Params suit-directive-copy-params current.params[k] = components[i].params[k] for k in l for i,l in arg

suit-condition-use-before Verify that the current time is BEFORE the specified time. suit-condition-use-before is used to specify the last time at which an update should be installed. The recipient evaluates the current time against the suit-parameter-use-before parameter (), which must have already been set as a parameter, encoded as seconds after 1970-01-01 00:00:00 UTC. Timestamp conditions MUST be evaluated in 64 bits, regardless of encoded CBOR size. suit-condition-use-before is OPTIONAL to implement.

suit-condition-image-not-match Verify that the current component does not match the suit-parameter-image-digest (Section 8.4.8.6 of ). If no digest is specified, the condition fails. suit-condition-image-not-match is OPTIONAL to implement.

suit-condition-minimum-battery suit-condition-minimum-battery provides a mechanism to test a Recipient's battery level before installing an update. This condition is primarily for use in primary-cell applications, where the battery is only ever discharged. For batteries that are charged, suit-directive-wait is more appropriate, since it defines a "wait" until the battery level is sufficient to install the update. suit-condition-minimum-battery is specified in mWh. suit-condition-minimum-battery is OPTIONAL to implement. suit-condition-minimum-battery consumes suit-parameter-minimum-battery ().

suit-condition-update-authorized Request Authorization from the application and fail if not authorized. This can allow a user to decline an update. suit-parameter-update-priority () provides an integer priority level that the application can use to determine whether or not to authorize the update. Priorities are application defined. suit-condition-update-authorized is OPTIONAL to implement.

suit-condition-version suit-condition-version allows comparing versions of firmware. Verifying image digests is preferred to version checks because digests are more precise. suit-condition-version examines a component's version against the version info specified in suit-parameter-version ()

suit-directive-wait suit-directive-wait directs the manifest processor to pause until a specified event occurs. Some possible events include: Authorization External Power Network availability Other Device Firmware Version Time Time of Day Day of Week

suit-directive-override-multiple This directive enables setting parameters for multiple components at the same time. This allows a small reduction in encoding overhead: without override-multiple, the encoding for each component consists of: set-component-index (2 bytes) override-parameters (1 byte + parameter map) with override-multiple, the encoding for each component consists of: the component index key (1 byte) the parameter map Override-multiple requires the command (1-2 bytes) and one additional map to hold the parameter sets (1 byte). For one component, there is no savings. For multiple components, there is an encoding savings of 2 bytes per component. Proper structuring of code should ensure that override-multiple follows a code-path nearly identical to set-component-index + override-parameters. This command is purely an encoding alias for set-component-index and override-parameters. The component index is set to the last component listed in the override-multiple argument when override-multiple completes. The following CDDL defines the argument for suit-directive-override-multiple: CDDL SUIT_Override_Mult_Arg = { uint => {+ $$SUIT_Parameters} }

suit-directive-copy-params suit-directive-copy-params enables a manifest author to specify one or more components to copy parameters from, and a list of parameters to copy from each specified source component. The behaviour is exactly the same as override parameters, but with parameter values defined in existing components. Parameters are only copied between identical keys (no copying from URI to digest, for example). For each entry in the map, the manifest processor sets the source component to be the component identified by the index contained in the map key. For each parameter identified in the copy list, the manifest processor copies the parameter from the source component to the current component. The following CDDL defines the argument for suit-directive-copy-params: CDDL SUIT_Directive_Copy_Params = { uint => [+ int] }

IANA Considerations IANA is requested to: allocate key 14 in the SUIT Envelope registry for suit-coswid allocate key 14 in the SUIT Manifest registry for suit-coswid allocate key 7 in the SUIT Component Text registry for suit-text-version-required allocate the commands and parameters as shown in the following tables

SUIT Commands Label Name Reference 4 Use Before 25 Image Not Match 26 Minimum Battery 27 Update Authorized 28 Version 29 Wait For Event

SUIT Parameters Label Name Reference 4 Use Before 26 Minimum Battery 27 Update Priority 28 Version 29 Wait Info

Security Considerations This document extends the SUIT manifest specification. A detailed security treatment can be found in the architecture and in the information model documents.

Fraunhofer SIT National Security Agency The MITRE Corporation National Institute of Standards and Technology ISO/IEC 19770-2:2015 Software Identification (SWID) tags provide an extensible XML-based structure to identify and describe individual software components, patches, and installation bundles. SWID tag representations can be too large for devices with network and storage constraints. This document defines a concise representation of SWID tags: Concise SWID (CoSWID) tags. CoSWID supports a similar set of semantics and features as SWID tags, as well as new semantics that allow CoSWIDs to describe additional types of information, all in a more memory efficient format. Arm Limited Arm Limited Fraunhofer SIT Inria Nordic Semiconductor This specification describes the format of a manifest. A manifest is a bundle of metadata about code/data obtained by a recipient (chiefly the firmware for an IoT device), where to find the that code/data, the devices to which it applies, and cryptographic information protecting the manifest. Software updates and Trusted Invocation both tend to use sequences of common operations, so the manifest encodes those sequences of operations, rather than declaring the metadata. Vulnerabilities in Internet of Things (IoT) devices have raised the need for a reliable and secure firmware update mechanism suitable for devices with resource constraints. Incorporating such an update mechanism is a fundamental requirement for fixing vulnerabilities, but it also enables other important capabilities such as updating configuration settings and adding new functionality.In addition to the definition of terminology and an architecture, this document provides the motivation for the standardization of a manifest format as a transport-agnostic means for describing and protecting firmware updates. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack.This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Arm Limited Arm Limited Fraunhofer SIT Vulnerabilities with Internet of Things (IoT) devices have raised the need for a reliable and secure firmware update mechanism that is also suitable for constrained devices. Ensuring that devices function and remain secure over their service lifetime requires such an update mechanism to fix vulnerabilities, update configuration settings, and add new functionality. One component of such a firmware update is a concise and machine-processable metadata document, or manifest, that describes the firmware image(s) and offers appropriate protection. This document describes the information that must be present in the manifest.

A. Full CDDL To be valid, the following CDDL MUST be appended to the SUIT Manifest CDDL. The SUIT CDDL is defined in Appendix A of

bstr) ; suit-coswid => bstr .cbor concise-software-identity) $$severable-manifest-members-choice-extensions //= ( suit-coswid => bstr .cbor SUIT_Command_Sequence / SUIT_Digest ) SUIT_Condition //= ( suit-condition-image-not-match, SUIT_Rep_Policy) SUIT_Condition //= ( suit-condition-use-before, SUIT_Rep_Policy) SUIT_Condition //= ( suit-condition-minimum-battery, SUIT_Rep_Policy) SUIT_Condition //= ( suit-condition-update-authorized, SUIT_Rep_Policy) SUIT_Condition //= ( suit-condition-version, SUIT_Rep_Policy) SUIT_Directive //= ( suit-directive-wait, SUIT_Rep_Policy) SUIT_Directive //= ( suit-directive-override-multiple, SUIT_Override_Mult_Arg) SUIT_Directive //=( suit-directive-copy-params, SUIT_Directive_Copy_Params) SUIT_Override_Mult_Arg = { + uint => {+ $$SUIT_Parameters} } SUIT_Directive_Copy_Params = { + uint => [+ int] } SUIT_Wait_Event = { + SUIT_Wait_Events } SUIT_Wait_Events //= (suit-wait-event-authorization => int) SUIT_Wait_Events //= (suit-wait-event-power => int) SUIT_Wait_Events //= (suit-wait-event-network => int) SUIT_Wait_Events //= (suit-wait-event-other-device-version => SUIT_Wait_Event_Argument_Other_Device_Version) SUIT_Wait_Events //= (suit-wait-event-time => uint); Timestamp SUIT_Wait_Events //= (suit-wait-event-time-of-day => uint); Time of Day (seconds since 00:00:00) SUIT_Wait_Events //= (suit-wait-event-day-of-week => uint); Days since Sunday SUIT_Wait_Event_Argument_Other_Device_Version = [ other-device: bstr, other-device-version: [ + SUIT_Parameter_Version_Match ] ] SUIT_Parameters //= (suit-parameter-use-before => uint) SUIT_Parameters //= (suit-parameter-minimum-battery => uint) SUIT_Parameters //= (suit-parameter-update-priority => uint) SUIT_Parameters //= (suit-parameter-version => SUIT_Parameter_Version_Match) SUIT_Parameters //= (suit-parameter-wait-info => bstr .cbor SUIT_Wait_Event) SUIT_Parameters //= (suit-parameter-component-metadata => bstr .cbor SUIT_Component_Metadata) SUIT_Parameter_Version_Match = [ suit-condition-version-comparison-type: SUIT_Condition_Version_Comparison_Types, suit-condition-version-comparison-value: SUIT_Condition_Version_Comparison_Value ] SUIT_Condition_Version_Comparison_Types /= suit-condition-version-comparison-greater SUIT_Condition_Version_Comparison_Types /= suit-condition-version-comparison-greater-equal SUIT_Condition_Version_Comparison_Types /= suit-condition-version-comparison-equal SUIT_Condition_Version_Comparison_Types /= suit-condition-version-comparison-lesser-equal SUIT_Condition_Version_Comparison_Types /= suit-condition-version-comparison-lesser suit-condition-version-comparison-greater = 1 suit-condition-version-comparison-greater-equal = 2 suit-condition-version-comparison-equal = 3 suit-condition-version-comparison-lesser-equal = 4 suit-condition-version-comparison-lesser = 5 SUIT_Condition_Version_Comparison_Value = [+int] SUIT_Component_Metadata = { ? suit-meta-default-permissions => SUIT_meta_permissions, ? suit-meta-user-permissions => SUIT_meta_permission_map, ? suit-meta-group-permissions => SUIT_meta_permission_map, ? suit-meta-role-permissions => SUIT_meta_permission_map, ? suit-meta-file-type => SUIT_Filetype, ? suit-meta-modification-time => CBOR_Datetime, ? suit-meta-creation-time => CBOR_Datetime, ? suit-meta-creator => SUIT_meta_actor_id, * $$SUIT_Component_Metadata_Extensions } SUIT_meta_permissions = uint .bits SUIT_meta_permission_bits SUIT_meta_permission_bits = &( write_attr_ex: 13, read_attr_ex: 12, sync: 11, delete: 10, recurse_delete: 9, write_attr: 8, change_owner: 7, change_perm: 6, read_perm: 5, read_attr: 4, creatdir_append: 3, list_read: 2, createfile_write: 1, traverse_exec: 0, * $$SUIT_meta_permission_bits_extensions ) SUIT_meta_permission_map = { + SUIT_meta_actor_id => SUIT_meta_permissions } SUIT_meta_actor_id = UUID_Tagged / bstr / str / int UUID_Tagged = #6.37(bstr) $$suit-text-component-key-extensions //= ( suit-text-version-required => tstr) suit-coswid = 14 suit-condition-use-before = 4 suit-condition-image-not-match = 25 suit-condition-minimum-battery = 26 suit-condition-update-authorized = 27 suit-condition-version = 28 suit-directive-wait = 29 suit-wait-event-authorization = 1 suit-wait-event-power = 2 suit-wait-event-network = 3 suit-wait-event-other-device-version = 4 suit-wait-event-time = 5 suit-wait-event-time-of-day = 6 suit-wait-event-day-of-week = 7 suit-parameter-use-before = 4 suit-parameter-minimum-battery = 26 suit-parameter-update-priority = 27 suit-parameter-version = 28 suit-parameter-wait-info = 29 suit-text-version-required = 7 ]]>